The invention relates to an integrated circuit having circuits that will be tested by an external test system, and to an external test system.
As a result of increasing complexity, testing integrated circuits is becoming more and more time-consuming. This leads to higher costs, and as a rule, reduces the throughput in the fabrication of integrated circuits. In order to reduce the test costs or to increase the throughput, it is necessary, for example, to increase the parallelism during testing. One further possibility is to reduce the requirements placed on the external test systems, in order in this way to reduce the test duration and therefore the costs.
For instance, a self-test (BIST=build-in self-test) is performed, during which the integrated circuits are tested by suitable additional circuits that are actually configured on the integrated circuit that will be tested.
Integrated circuits can exhibit an increased current consumption because of defects such as short circuits or within the context of process fluctuations in fabrication. In order to identify corresponding chips, it is necessary to measure a current flow through the entire integrated circuit or parts thereof during the production test. This current measurement has hitherto been carried out by a DC measurement unit. For this purpose, an appropriately equipped external test system is required which, during the parallel testing, needs a separate measuring unit for each of the integrated circuits that will be tested.
It is accordingly an object of the invention to provide an integrated circuit in which the current consumption can be measured more quickly during testing and in which lower requirements are placed on the external test system. It is furthermore an object of the present invention to provide a method for measuring current in such an integrated circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, an integrated circuit, including: a circuit having a current flowing therein; an external connection; and a current measuring unit for obtaining a measured current representing the current flowing in the circuit. The current measuring unit includes an output device for outputting a value of the measured current to an external test system via the external connection. The current measuring unit includes a measurement current path. The current measuring unit includes a current measuring circuit. The current measuring unit includes a current mirror circuit for obtaining a mirrored current by mirroring the current flowing in the circuit into the measurement current path. The measurement current path is led through the current measuring circuit so that the measured current can be obtained by measuring the mirrored current and so that the value of the measured current can be output by the output device. The current measuring circuit includes a capacitor. The current measuring circuit includes a switching device for charging the capacitor from a low voltage value to a high voltage value by using the mirrored current and for reversing a polarity of the capacitor when a voltage value stored in the capacitor exceeds the high voltage value. A number of charging operations of the capacitor occurring during a predetermined time period depend in an unambiguous way on the mirrored current.
In accordance with an added feature of the invention, the current measuring circuit has a counter device designed to measure the number of the charging operations of the capacitor occurring during the predefined time period; and the counter device outputs the number of the charging operations via the output device.
In accordance with an additional feature of the invention, there is provided, a second current measuring circuit including a second switching device, a second capacitor, and a second counter device. The second current measuring circuit obtains a predetermined current. The second capacitor is charged by the predetermined current for a predetermined number of recharging operations of the second capacitor. The second counter device is connected to the first current measuring circuit for starting the first counter device to begin counting the predetermined number of charging operations of the second capacitor and for stopping the first counter device after the predetermined number of recharging operations of the second capacitor has been reached.
In accordance with another feature of the invention, the output device is configured to serially transmit the value of the measured current to the external test system.
In accordance with a further feature of the invention, the integrated circuit includes a DRAM memory circuit.
In accordance with a further added feature of the invention, the current measuring circuit has a capacitor that can substantially be charged up via the mirrored current.
In accordance with another added feature of the invention, the output device is configured to output the measured value as a digital value.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of measuring a current in a circuit in an integrated circuit. The method includes steps of: providing the integrated circuit with a current measuring unit including a current mirror circuit for mirroring the current in the circuit into a measurement current path; providing the current measuring unit with an output unit to output a measured value of a measured current via an external connection; providing a voltage to the integrated circuit which lies a predetermined amount above a nominal supply voltage of the integrated circuit, the predetermined amount corresponding to a voltage drop across a transistor in the integrated circuit; and obtaining the measured value in dependence on a current consumption of the circuit.
In accordance with an added mode of the invention, the method includes steps of: outputting a reference current to the integrated circuit; and determining the measured value by using the reference current and outputting the measured value with the output device.
According to the invention, an integrated circuit is provided with a circuit that has a current measuring unit. The current measuring unit is used to measure the current through the circuit, and the current measuring unit is connected to an output device. The output device is configured in such a way that the value of the measured current can be output to an external test system via an external connection of the integrated circuit.
According to the invention, therefore, the current measuring unit is provided within the integrated circuit instead of, as had customarily been the case, providing the current measuring unit outside the integrated circuit, for example, in the external test system or connected to the external test system. In this way, the current through the circuits of the integrated circuit can be measured at any time, so that during the parallel testing of a plurality of integrated circuits, the current through the circuits of each of the integrated circuits can be measured substantially simultaneously in each case and can subsequently be transmitted to an external test system, for example. This therefore avoids the necessity of providing an additional current measuring unit outside the integrated circuit, in which the current measurements would have to be carried out sequentially if a sufficient number of external current measuring devices are not available.
Since it is frequently customary to provide integrated circuits with a BIST circuit, a data output used by the BIST circuit can also be used to output the current value.
A further advantage resides in the fact that, during the current measurement, a common voltage source can be used for a plurality of integrated circuits that will be tested in parallel. Individual voltage sources for an external current measuring unit in each case are therefore not necessary.
Provision can preferably be made for the output device to be configured to transmit the value of the measured current serially to an external test system. This has the advantage that the current value can be output via only one output connection, so that the remaining connections continue to be available for testing the functionality of the circuit. That is to say, the current is measured during a functional test of the circuit, and the corresponding current value is read out during the testing of the functional circuits.
The circuits of the integrated circuit can include a memory circuit. In particular in the case of memory circuits, the current flow is a significant variable that determines the quality and classification of the memory circuit, in particular in the case of DRAM modules. Since the value of the current must not exceed a specific amount and depends on the operating frequency, the maximum permissible current, in addition to other influencing variables, determines the maximum operating frequency of the memory module. In this case, the maximum operating frequency is often used as a classification feature, and chips with an increased current consumption are sorted out with regard to the specification.
The current measuring unit preferably has a current measuring circuit and a current mirror circuit, in order to mirror the current through the circuit into a measurement current path. The measurement current path is led through a current measuring circuit, in order to measure the mirrored current and to output the value of the measured current via the output device. In this way, the current measuring unit only influences the circuit to a low extent, so that the current that flows through the circuit can be measured exactly.
Additionally, the current measuring circuit can have a switching device with a capacitor, in order to charge up the capacitor from a low voltage value to a high voltage value using the current and in order to reverse the polarity of the capacitor when the voltage value stored in the capacitor exceeds the high voltage value. A number of charging operations of the capacitor occurring during a predetermined time period depend on the current. In this way, a current measuring circuit can be implemented which measures the current as a number of charging operations. This has the advantage that such a switching device can be implemented in a particularly simple way in an integrated circuit. Furthermore, using the switching device, the value of the current that is measured can be digitized in a particularly simple way.
Furthermore, the current measuring circuit can have a counter device that is designed to measure the number of charging operations of the capacitor during a predefined time period and to output the measured number of charging operations via the output device. In this way, the value of the current that is measured can be averaged during the predefined time period, so that an average current flow is measured, in which short-term disruption, for example, interference pulses, remains unnoticed.
Furthermore, the integrated circuit can have a second current measuring circuit that includes a second switching device with a second capacitor and a second counter device. In this case, a predetermined current, which is provided, for example, by the external test system, is applied to the second current measuring circuit. The second capacitor can be charged up by the predetermined current for a predetermined second number of charging operations. The second counter device is configured in such a way that, at the start of counting the predetermined second number of charging operations in the second capacitor, the second counter device starts the predefined time period in the first counter device, and after reaching the predetermined second number of charging operations of the second capacitor, the second counter device stops the predefined time period in the first counter device. The second counter device therefore counts a predefined number of charging operations by using a current of known magnitude, which is externally applied, for example. The starting and reaching of the final value of this second counter device are used to define the time during which the first counter determines the number of charging operations by the current that is measured. In this way, the absolute value of the current that is measured through the circuit can be determined, and only the following parameters have to be known: the current through the second current measuring circuit, which is predetermined by the external test system for example, the ratio of the first capacitance to the second capacitance, and also the predetermined second number of charging operations. Therefore, only the capacitance ratio is needed as a component parameter.
According to a further aspect of the present invention, an external test system for measuring a current in an integrated circuit can be provided. The external test system is configured in order to output a voltage to the integrated circuit. The voltage is a predetermined amount above the nominal supply voltage of the integrated circuit. The external test system is also configured to receive a measured value that depends on the current consumption of the integrated circuit.
Providing a circuit for measuring a current in an integrated circuit means that the external test system does not have to carry out its own current measurement, but merely receives the measured value that indicates the current consumption of the circuit. The external test system can therefore receive the corresponding measured values in parallel, and does not have to carry out a measurement one after another during parallel testing. If the measured value is transmitted as a digital value, it is possible to dispense with analog measuring devices in the external test system. Furthermore, provision can be made for the external test system to output a reference current, and it is possible for the current that is measured to be determined using the reference current, the predetermined second number of recharging operations, the capacitance ratio of the first capacitor to the second capacitor and the first number of recharging operations that correspond to the measured value.
The magnitude of the externally applied voltage is advantageously chosen in such a way that a voltage drop across the current mirror circuit is compensated for and the circuit is supplied with the nominal voltage.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a integrated circuit having a current measuring unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.